This study is directed toward obtaining a better understanding of the blood-materials interaction in human synthetic vascular grafts. Sensitive, specific and quantitative tests to detect thrombin formation, thrombin action and platelet activation in patients receiving vascular grafts will be used to determine hemostatic variations resulting from the acute phase of the blood-materials interaction. Correlative analyses of preclotted grafts and in vitro studies of blood and its components with clean, preclotted and retrieved grafts will be carried out. These studies will permit elucidation of the early phase of the blood-materials interaction of a clinically efficacious material. In human vascular grafts, the composition and extent of pseudointima will be determined with special attention directed toward the relationship with the extent and patterns of endothelialization and fibrinolytic activity. An integrated program, which makes use of the computer data bank of the Cleveland Vascular Society, will permit prospective and retrospective studies of human vascular grafts.